Polishing apparatus

ABSTRACT

A polishing apparatus comprises a polishing member that has a wide stable polishing range to perform effective polishing, even if a rotation axis moves away from the edge of a workpiece. A polishing member holder holds the polishing member, and a workpiece holder holds the workpiece to be polished. A drive device produces a relative sliding motion between the polishing member and the workpiece. At least one holder of either the polishing member holder or the workpiece holder is rotatable about a rotation axis and is tiltable with respect to other holder. Such one holder is provided with a pressing mechanism to stabilize orientation or desired posture of the one holder by applying an adjusting pressure to the one holder at a location away from the rotation axis.

[0001] This is a divisional of application Ser. No. 09/296,567, filedApr. 22, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an apparatus for polishingworkpieces such as semiconductor wafers, various kinds of hard disks,glass substrates and liquid crystal display panels.

[0004] 2. Description of the Related Art

[0005] In a conventional chemical mechanical polishing (CMP) apparatusused in fabrication of a semiconductor integrated circuit, asemiconductor wafer is held by a holder called a “top ring” and isrotated and pressed against a polishing cloth mounted on a rotatingturntable while being supplied with abrading slurry including freeabrading grains at a sliding interface. However, such a CMP apparatuspresents a problem that, depending on the type of surface patterns anddifferences in the heights of fine surface structures fabricated on thewafer, it is not possible to obtain a precisely polished flat surface.

[0006] Therefore, in place of the above-mentioned CMP process, anotherCMP technique has been developed, where the wafer is placed in slidingcontact with a solid polishing member shaped usually in the form of aplate, in which abrading grains are bound in a matrix, while a polishingliquid or a polishing solution is supplied at the sliding interface. Thesolid polishing members include variations such as a ring-type member ora cup-type member having abrading pellets distributed in a ring shape.

[0007]FIG. 11 illustrates basic movements of a cup-type polishingmember. A cup-type polishing member 80 has a ring-shaped abrading member81 attached on the bottom surface of a polishing member holder 83, andis pressed against a wafer 100 held in a wafer holder 85. Both arerotated, for example, in the same G, H directions, and the wafer 100 isuniformly polished by moving the polishing member 80 linearly in theradial direction of the wafer 100 (indicated by the arrow I) so that theabrading member 81 polishes the entire surface of wafer 100. Thepolishing member holder 83 is connected to the drive shaft 89 through aspherical bearing 87 so as to transmit a pressing force F from the driveshaft 89 through the spherical bearing 87, and coupling of drive pin 91passive pin 93 transmits the rotation H from the drive shaft 89.

[0008] In general, the polishing member 80 is pressed on the wafer 100through the drive shaft 89, therefore, when drive axis k of the driveshaft 89 is projected within the wafer 100, as shown in FIG. 11, thereis no tilting of the polishing member 80. But, when it is in theposition shown in FIG. 12, the rotation axis k projects outside thewafer 100, and even if a part of the abrading member 81 is on the wafer,A lever action produces tilting of the abrading member 81 about fulcrumat the edge of the wafer 100. This prevents the abrading member 81 fromhaving a planar contact with the wafer 100, and polishing becomesimpossible. Therefore, to avoid such a situation, conventional abradingmember 81 could only move within an area of support for the drive axisk. This problem is the same in a conventional polishing apparatus usinga top ring holding the wafer to press it against a polishing table.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a polishingapparatus using a polishing member that has a wide stable polishingrange to perform effective polishing, even if the rotation axis movesaway from the edge of a workpiece to be polished.

[0010] The object has been achieved in a polishing apparatus comprisedby a polishing member holder for holding a polishing member and aworkpiece holder for holding a workpiece to be polished; and a drivedevice to produce a relative sliding motion between the polishing memberand the workpiece; wherein at least one holder of either the polishingmember holder or the workpiece holder is rotatable about a rotation axisand is tiltable with respect to other holder, and the one holder isprovided with a mechanism to stabilize orientation or desired posture ofthe one holder by applying an adjusting pressure to the one holder at alocation away from the rotation axis.

[0011] The polishing apparatus of such a construction can maintain astable contact of the workpiece to be polished to the polishing memberat all times to produce stable polishing, even when a projected line ofthe rotation axis is outside the workpiece to be polished, therebywidening the relative movable range of the polishing member to theworkpiece and providing an increased selection for controllingparameters or controlled systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a perspective view of a first embodiment of A polishingapparatus;

[0013] FIGS. 2A-2C are illustrations of the movement of the apparatusshown in FIG. 1;

[0014] FIGS. 3A-3C are graphs to illustrate pressure mechanisms;

[0015] FIGS. 4A-4C are illustrations of a second embodiment;

[0016]FIG. 5 is a side view of a second embodiment of the polishingapparatus;

[0017]FIGS. 6A, 6B are, respectively, a side view and a plan view of athird embodiment;

[0018]FIG. 7 is a side view of a fourth embodiment of the polishingapparatus;

[0019]FIG. 8 is a side view of a fifth embodiment of the polishingapparatus;

[0020]FIG. 9 is an illustration of the contact of a polishing member ona surface of a wafer to be polished;

[0021]FIG. 10 is a side view of a sixth embodiment of the polishingapparatus;

[0022]FIG. 11 is an illustration of the action of a conventionalpolishing apparatus; and

[0023]FIG. 12 is an illustration of problems associated with theconventional polishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Preferred embodiments will be presented with reference to thedrawings.

[0025]FIG. 1 shows a perspective view of an overall polishing apparatushaving a solid polishing member according to the first embodiment of thepresent invention. The apparatus comprises a base plate 30, a table 40moving linearly in the direction C by a drive mechanism (not shown), awafer holder 45 disposed on the table 40; a polishing member 10 disposedat the end of a drive shaft 50 extending from the bottom surface of asupport arm 31.

[0026] The wafer holder 45 has a wafer holding section for holding thewafer 100, and is rotated by a drive mechanism provided inside the table40. The polishing member 10 has a ring-shaped abrading member 11 (orpellet-like abrading member arranged in a ring shape) on the bottomsurface of a polishing member support disk (polishing member holder) 13,and is rotated by the shaft 50. Between the drive shaft 50 and thepolishing member 10, a spherical bearing 52 (FIG. 2A) is provided fortransmitting a pressing force from the drive shaft 50 to the polishingmember 10. Also, drive pins and passive pins (not shown) are providedfor transmitting rotation from the drive shaft 50 to the polishingmember 10, as in the conventional polishing apparatus shown in FIGS. 11,12. The pressure against the wafer is mainly applied by the drive shaft.

[0027] On both sides of the shaft 50, pressing devices 20 each having atop end fixed to a side surface at the distal end of the support arm 31are provided. Each pressing device 20 has a pressing cylinder 21, a rod23 extending therefrom, and a rotatable roller 25 disposed at the bottomend of the rod 23. The rollers 25 are on opposite sides of and straddlethe rotation axis of the polishing member 10, relative to direction C oflinear movement of the polishing member 10, and the rolling surfaces runalong the circumferential periphery of the polishing member 10 so as topress on the back surface (top surface in FIG. 1) of the polishingmember 10 near its edge. It is permissible to provide one or more thanthree pressing devices 20.

[0028] Pressing cylinders (only one is shown in FIG. 1) 21 haverespective pressure control units 27, 28, and share a control section 29(having CPU and other components) to output control signals for theunits 27, 28. Table 40 is provided with position sensors to detect theposition of the table 40. A pressing pressure control section is thuscomprised by the control section 29, pressure control units 27, 28 andposition sensors disposed on the table 40.

[0029] The operation of the apparatus will be explained with referenceto FIG. 2. First, the wafer holder 45 and the polishing member 10 areindependently rotated in the respective A, B directions, and the table40 is linearly and reciprocatingly moved along the direction C toperform uniform polishing of the overall surface of the wafer 100 withthe abrading member 11.

[0030] The control section 29 detects the positions of the table 40 andthe polishing member 10 according to signals output by the positionsensors, and outputs control signals to pressure control units 27, 28.As illustrated in FIG. 2A, not only when the polishing member 10 isentirely situated within the wafer 100, but even when a part of thepolishing member is extending out of the wafer 100, as illustrated inFIG. 2B, there is no danger of the polishing member 10 tilting, so thatcontrol signals are output in such a way that the pressure control units27, 28 produce the same pressures.

[0031] On the other hand, when the control section 29 detects, from theposition sensor signals on the table 40, that the rotation axis of thepolishing member 10 is outside the periphery of the wafer 100, asillustrated in FIG. 2C, the control section 29 outputs control signalsto pressure control units 27, 28 so that they will be outputtingdifferent pressures against the polishing member 10 through therespective cylinders 21. In other words, pressing pressure of thepressing device 20 for the on-wafer side is made higher relative to thatfor the off-wafer side. In this manner, the application point of abalancing or leveling pressure will always be projected on the wafer100, and there will be no tilting of the polishing member 10. Rotationof the polishing member 10 is not affected adversely by the pressingdevice 20 because the pressure of cylinders 21 is applied to the backsurface of the polishing member 10 through friction reducing rollers 25.

[0032] FIGS. 3A-3C show a pressure control methodology using thecylinders 21. The horizontal axis of all the graphs relates to relativepositions of wafer and abrading member, and on the vertical axis, FIG.3A shows ratios of contact area of abrading member to wafer; FIG. 3Bshows ratios of pressures in the pressing cylinders; and FIG. 3C showsrespective cylinder pressures.

[0033] As shown in FIG. 3A, when the rotation axis m of the polishingmember 10 is near the central area of the wafer 100, the total surfacearea of the abrading member 11 is in contact with the wafer 100. Whenthe polishing member 10 moves to the left or the right to overhang fromthe edge of the wafer 100, the contact area between the abrading member11 and the wafer changes rapidly. Therefore, in order to maintain thepressure of abrading member 11 on the wafer constant, the pressing forceexerted on the polishing member 10 must be reduced accordingly.

[0034] As shown in FIG. 3B, when the rotation axis m of the polishingmember 10 moves away from the edge of the wafer 100, the off-wafer sidepressing device 20 must exert less pressure relative to the on-waferside pressing device 20. The two pressing devices 20 are operated insuch a way that the further the polishing member 10 is away from theedge of the wafer 100 the higher the ratio of the pressures in the twopressing devices 20 so as to maintain a balancing pressure within thewafer 100.

[0035] As shown in FIG. 3C, the magnitude of the pressure is maintainedthe same in each pressing device 20 when the rotation axis m is locatedwithin the wafer 100, but as the rotation axis m moves away from theedge of the wafer, the pressure in the on-wafer side pressing device 20is made higher than that in the off-wafer side pressing device 20. Asthe rotation axis m moves further away from the edge of the wafer 100,pressures are altered as shown in FIG. 3C, so that the actual magnitudeof the pressure will be adjusted according to the ratios of thepressures as seen in FIG. 3B at corresponding relative locations of theabrading member 11 and the wafer 100.

[0036] Accordingly, even when the rotation axis m moves off the edge ofthe wafer 100, it is possible to control the orientation or desiredposture of the abrading member 11 to abrade on the wafer 100, therebyexpanding the operational range of the polishing member 10.

[0037] The same effect can be achieved by using magnetic bearings. FIGS.4A-4C show examples of the use of different types of magnetic bearings.A pair of magnetic bearings 121, 121 a, 121 b are used as shown in FIGS.4A-4C to non-contactingly support abrading member support disk 13 e tobalance the load on polishing member 10 e. In FIG. 4B, the balancingmechanism is provided on a cylindrical portion of the abrading membersupport disk 13 e. Such arrangements of paired magnetic bearings 121,121 a, 121 b are effective in leveling the abrading member support disk13 and expand the operational control range of the polishing member 10.

[0038]FIG. 5 shows essential parts of a second embodiment of polishingmember 10 a and pressing devices 20 a. This polishing member 10 aincludes an abrading member support disk 13 a and a ring-shaped abradingmember 11 a (or pellet-like abrading member arranged in a ring shape)and is provided with an outer edge or brim section 15 a around thecircumference of the disk 13 a that is outside the abrading member 11 a.In this case, shaft 50 a is used only to support the polishing member 10a and is not rotated.

[0039] The pressing devices 20 a comprises a pair of upper rollers 25 aand a pair of lower rollers 26 a, each provided at the end of a rod 23 aextending from the bottom of a respective pressing cylinder 21 a. Leftand right pairs of upper and lower rollers 25 a, 26 a are used to clampthe brim section 15 a. One upper roller 25 a is rotated by an abradingmember drive motor 27 a provided on the outside of the respectivepressing device 20 a.

[0040] In this polishing member 10 a, abrading member drive motor 27 ais operated to rotate the polishing member 10 a, and concurrently thepressures of the pressing devices 20 a are individually adjusted tomaintain the polishing member 10 a in a level position or desiredposture even if the rotation axis m of the polishing member 10 a movesaway from the edge of the wafer 100.

[0041]FIGS. 6A, 6B show essential parts of a third embodiment ofpolishing member 10 b and three pressing devices 20 b in aside view inFIG. 6A, and in a plan view in FIG. 6B. The polishing member 10 b is thesame as the polishing member 10 a shown in FIG. 5, and comprises anabrading member 11 b attached to the bottom surface of an abradingmember support disk 13 b, and a brim section 15 b on the edge of theabrading member support disk 13 b. However, this polishing member 10 bdoes not have a shaft 50 a shown in FIG. 5.

[0042] The pressing device 20 b is also the same as the pressing device20 a shown in FIG. 5, and comprises upper and lower rollers 25 b, 26 battached to the end of a rod 23 b so as to clamp the brim section 15 b,and one of the pressing rollers 20 b is provided with a drive motor 27b. In this embodiment, each pressing device 20 b is provided, at the endof the respective rod 23 b, with an edge guide roller 17 b to guide theabrading member support disk 13 b, by contacting the outer verticalperiphery of the disk 13 b.

[0043] In effect, the shaft 50 a for supporting the polishing member 10a in the second embodiment is replaced with the edge guide rollers 17 bin this embodiment. The polishing member 10 b is rotated by operatingthe abrading member drive motor 27 b, and concurrently, individualpressures in the pressing devices 20 b are adjusted to maintain thepolishing member 10 b in a level position or desired posture even if therotation axis m of the polishing member 10 b moves away from the edge ofthe wafer 100, as in the second embodiment.

[0044]FIG. 7 shows a schematic side view of pressing devices 20 c forleveling a polishing member 10 c in a fourth embodiment. The polishingmember 10 c is the same as the polishing member 10 a shown in FIG. 5 andcomprises an abrading member 11 c attached to the bottom surface of anabrading member support disk 13 c, and a brim section 15 c on the edgeof the abrading member support disk 13 c. In this case, shaft 50 csupports and rotates the polishing member 10 c. Each pressing device 20c is provided with only a lower roller 26 c provided at the end of a rod23 c, extending from the bottom of a respective pressing cylinder 21 c,to contact the bottom surface of the brim section 15 c.

[0045] In this embodiment, the polishing member 10 c is rotated byrotating the shaft 50 c, and concurrently, each of the pressing devices20 c is adjusted to vary the lift force exerted through the rod 23 c tomaintain the polishing member 10 c in a level position or desiredposture even if the rotation axis m of the polishing member 10 c movesaway from the edge of the wafer 100, as in the second embodiment.

[0046]FIG. 8 shows a schematic side view of pressing devices 20 d forleveling a polishing member 10 d in a fifth embodiment. The polishingmember 10 d is the same as the polishing member 10 a shown in FIG. 5 andcomprises an abrading member 11 d attached to the bottom surface of anabrading member support disk 13 d, and a brim section 15 d on the edgeof the abrading member support disk 13 d which is rotated with a shaft50 d. The pressing device 20 d is the same as the pressing device 20 cshown in FIG. 7, and is provided with only a lower roller 26 d providedat the end of a rod 23 d, extending from the bottom of a respectivepressing cylinder 21 d, to contact the bottom surface of the brimsection 15 d.

[0047] In this embodiment, two position sensors 60 are provided near theedge of the top surface of the polishing member 10 d, and signals outputfrom the position sensors 60 are input in a position sensor signalamplification circuit 63 in a control device 61, and a pressing cylinderdrive circuit 67 outputs control signals to the pressing cylinders 21 daccording to an abrading member tilt computation section 65.

[0048] In this embodiment, polishing is performed with the polishingmember 10 d inclined at angle θ to the wafer 100, as shown in FIG. 8.Regardless of the location of the rotation axis m of the polishingmember 10 d, pressure values for the pressing cylinders 21 d arecomputed and controlled so that, in this case, the vertical distancebetween the right position sensor 60 and the polishing member 10 d islonger than the distance between the left position sensor 60 and thepolishing member 10 d.

[0049] By controlling the pressing cylinders 21 d in this manner, theabrading member 11 d is tilted at a given angle, and moves over thesurface of the wafer 100 while maintaining such tilt or desired posture.The reason for tilting the abrading member 11 is as follows. When theabrading member 11 d is made to contact the wafer 100 at a given angle,as illustrated in FIGS. 8 and 9, because of a specific elasticity of theabrading member 11 d, contact occurs not over a line contact but over acontact area S. The contact area S is always a specific constant value,no matter where the abrading member 11 is moved over the wafer 100.Therefore, uniform polishing of the entire surface of the wafer may beachieved easily, by controlling the feed speed of the abrading member 11d, and because the contact area S is always constant, pressure controlis simplified.

[0050] In contrast, when the entire abrading surface of the abradingmember 11 d is in contact with the wafer 100, the contact area variesdepending on where the abrading member 11 d is on the wafer so that thecontrol parameters (feed speed for abrading member 11 d and pressingpressure on abrading member 11 d) to provide uniform polishing becomemore complex.

[0051] The control method based on position sensors 60 and the controldevice 61 can be applied to the foregoing first to fourth embodiments.In other words, the method is equally applicable when it is not desiredto tilt the polishing member. Also, the above embodiments each utilizesa cup-type abrading member (11, 11 a, 11 b, 11 c, 11 d), but a disc-typeabrading member can be used to produce the same effects.

[0052] Locations for applying balancing pressure and the number ofpressing devices are not limited to those demonstrated in the foregoingembodiments, and they can be changed to suit each application, forexample, the pressing location may only be one location. In the case offirst to third embodiments, the abrading member is pushed towards theworkpiece to be polished, therefore, when the rotation axis projects offthe wafer, it is necessary to press on any area still remaining on theworkpiece by lowering the pressing cylinders. On the other hand, infourth and fifth embodiments, the abrading member is forced to be liftedaway from the workpiece so that, when the rotation axis projects off theworkpiece, it is necessary to lift any area that is off the workpiece byraising the pressing cylinders. The important point is to adjust thepressing devices in such a way that even though the rotation axis may beoff the workpiece, the point of applying a balancing pressure is alwaysprojected within the workpiece.

[0053] Also, in the fifth embodiment, pressing devices 20 d werecontrolled according to position sensors 60, but the pressures of thepressing devices 20 d can be controlled by using other sensing meanssuch as to directly detect the tilting angle of the cup-type abradingmember 10 d.

[0054] In some cases, the conventional CMP process may be applied eitherbefore or after the polishing process based on the abrading memberaccording to the present invention.

[0055]FIG. 10 shows a schematic side view of a sixth embodiment of thepolishing member used in conjunction with a combination of a turntableand a top ring. The polishing apparatus comprises a rotating turntable71 and a polishing cloth (polishing tool) 72 mounted on top thereof, anda rotating top ring 73 holding a wafer (workpiece) 74 in the bottomsection to press against the polishing cloth 72. Polishing is performedusing a polishing solution including free abrading grains suspendedtherein. As in the first embodiment, a pair of pressing devices 76 areprovided for balancing purposes so as to straddle the rotation axis o ofthe top ring 73. In this example, they are disposed symmetrically acrossthe rotation axis o. The pressing devices 76 can be selected from manychoices including hydraulic pressure devices based on water or oil orair, and balance control may be achieved by elasticity, piezoelectriccontrols and others means.

[0056] In this case, the top ring 73 is rotated by a rotation shaft 75and, at the same time, is pressed against the wafer 73 by the twopressing devices 76. This arrangement is effective in providing balancedpolishing or desired posture, even when the rotation axis o is off theedge of the table 71, by adjusting the pressures in the pressing devices76 so as to maintain the projected point of applying a balancingpressure for the top ring 73 within the turntable 7 to prevent tiltingof the top ring 73.

[0057] Polishing cloth 72 may be replaced with a polishing member ofvarious types such as an abrasive stone. Locations of the pressingdevices 76 and their designs may be changed to suit each application.The number of pressing devices may be varied from a minimum of onedevice to more than three devices. Also, the pressing devices 76 may bemade in the same manner as those in the second to fifth embodiments.

What is claimed is:
 1. A polishing apparatus for polishing a surface ofa workpiece, said apparatus comprising: a workpiece holder to hold aworkpiece to be polished; a polishing member holder to hold a polishingmember having a polishing surface in opposition to the workpiece, thepolishing surface being directed upwardly; a polishing pressure applyingdevice to press against each other under pressure confronting surfacesof the workpiece and the polishing member; and a drive device to producerelative motion between the confronting surfaces of the workpiece andthe polishing member, thus to polish the surface of the workpiece.
 2. Apolishing apparatus as claimed in claim 1 , wherein said relative motionis produced by a combination of linear motions.
 3. A polishing apparatusas claimed in claim 1 , further comprising a mechanism for moving thepolishing member to allow at least part of the polishing member toproject from an outer periphery of the workpiece.
 4. A polishingapparatus for polishing a surface of a workpiece, said apparatuscomprising: a polishing member which is rotatable and has a polishingsurface directed downwardly; a drive device to produce relative motionbetween the confronting surfaces of the workpiece and the polishingmember; and a polishing pressure applying device to press against eachother the confronting surfaces of the workpiece and the polishing memberby pressing the polishing member at a position other than a rotatingaxis of the polishing member.